Williamson County, Texas septic permits and requirements

Permitting authority

Williamson County Department of Infrastructure — County Engineer’s Office, On-Site Sewage Facility Program

Williamson County Department of Infrastructure, 3151 SE Inner Loop, Suite B, Georgetown, TX 78626; OSSF office 512-943-3330. Confirm jurisdiction and current office procedures before visiting.

Williamson County Engineer’s Office is the local OSSF authority except within the City of Austin

Williamson County Environmental Services states that its OSSF program regulates septic systems throughout Williamson County except areas located within the City of Austin. The County Engineer’s Office is authorized by TCEQ to administer the local program under 30 TAC Chapter 285 and the Williamson County OSSF Order. Owners near municipal boundaries should confirm jurisdiction before applying.

New systems, repairs and enlargements use the county’s online permit process

Williamson County requires an application to install a new OSSF or to modify, repair or enlarge an existing system. Applications are submitted through MyGovernmentOnline; the county says it no longer accepts paper or emailed OSSF applications. When the property footprint changes, a Certificate of Compliance must be obtained before the OSSF application can be processed, while a proposed OSSF in a floodplain requires a Floodplain Permit instead of that certificate.

The application package requires a soil evaluation, site plan and complete OSSF design

The county’s application checklist requires a warranty deed, owner authorization when an agent applies, a survey when the property is not in a recorded subdivision, a complete OSSF design, a separate soil-evaluation report, a separate site-plan overview and a floor plan. The checklist says proprietary or non-standard designs, designs over the Edwards Aquifer Recharge Zone, and designs in the 100-year floodplain must be submitted by a Texas Registered Sanitarian or Professional Engineer.

Current county permit fees range from $510 for residential conventional systems to $910 for commercial aerobic systems

Williamson County’s OSSF fee sheet, updated September 12, 2025, lists $510 for a residential conventional permit, $610 for residential non-conventional/non-aerobic, $710 for residential aerobic treatment or other routine-maintenance systems, $810 for commercial non-aerobic, and $910 for commercial aerobic/routine-maintenance systems. It also lists $100 for an extra site visit or inspection, $150 for a new or additional design review, and $60 for an aerobic-system license renewal or transfer. Applicants should confirm the live county fee sheet before paying because schedules can change.

County inspections occur during critical construction phases before final approval

Williamson County publishes system-specific inspection sequences. Most systems include two inspections; for example, conventional and leaching-chamber systems are inspected at the tank/pipe-and-gravel stage and again at final landscaping, while aerobic systems are inspected with tanks and lines open and again at final electrical/landscape completion. The licensed installer must schedule inspections and be present with equipment to verify construction elevations. Homeowners seeking to install their own residence system must obtain written county approval and follow the inspection schedule issued by the county.

Aerobic and other routine-maintenance systems require continuing maintenance documents

For an aerobic or other routine-maintenance OSSF, the county application requires a maintenance contract signed by both the owner and maintenance provider plus a recorded maintenance affidavit. Williamson County says its aerobic systems are initially permitted for two years and that owners must maintain a valid service arrangement and renew the county OSSF license at least every two years. The county currently charges $60 for that renewal.

Aerobic licenses must be transferred when the property changes ownership

Williamson County instructs a buyer of property with an aerobic system to transfer the operating license to the new owner. The county currently lists a $60 transfer fee and provides a License Renewal / Transfer form. Owners should also make sure the required maintenance arrangement remains in place through the transfer.

Unlicensed existing systems may require a permit and compliance work

The current fee schedule specifically addresses inspection of an unlicensed OSSF and states that the owner must purchase the appropriate OSSF permit and bring the system into compliance if the system is found to be illegal. Because repairs and enlargements also require applications, owners should contact the county before uncovering, replacing or modifying an existing system.

Septic permit records can be requested directly from the county

Williamson County accepts OSSF open-records requests for septic information. The county asks requesters to provide the property address or property ID and, when available, subdivision lot/block information or prior owner names so staff can locate the permit record.

Official sources

SepticScope summarizes public-agency information for planning purposes. The permitting agency's current instructions control if they differ from this guide.

Report outdated county information

Septic rules, forms and agency pages can change. If you find a broken official link or a county requirement that has changed, send SepticScope feedback and include the current local government source.